A glass making apparatus for delivering high quality glass in the manufacture of precision glass articles requires careful attention to the delivery systems. Such precision products can include optical lenses and glass panels for the manufacture of display devices such as televisions, computers, cell phones, etc.
Molten glass delivery systems for high precision products may typically be formed from precious metals, and usually platinum or platinum alloys such as a platinum rhodium alloy. Such precious metals, usually selected from the platinum group of metals, have high melting temperatures, and are less likely to contribute contaminants to the molten glass (melt) flowing through these “platinum” delivery systems. In many instances, individual components of a particular platinum delivery system, a finer for example, or a stirring vessel, are produced by joining multiple subcomponents. For example, a cylindrical tube might be formed by rolling several flat platinum plates into semicircular segments, then welding the segments to form the tube. In another example, stirrers for stirring the molten glass may be formed by welding individual stirring blades to a shaft. Even the shaft may be formed from multiple components.
In spite of the relatively benign behavior of platinum (or platinum alloy) when submerged within the corrosive molten glass, it has been found that some of these platinum components may be contributing to inadvertent contamination of the molten glass with gaseous inclusions, or blisters.
Blisters believed to originate from precious metal components, such as an apparatus for stirring molten glass, have been identified as a significant loss issue in the manufacture of glass sheet for LCD display substrates. The problem is especially prevalent during startup of a melting furnace, but has also been observed mid-campaign. Because the defects constitute greater than about 90% CO2, the underlying problem is believed to be carbon contamination of the components. The carbon contamination may be present in the components as-received from the component manufacturer, or it might be introduced into the component during operation.
The following disclosure addresses treating individual components and/or sub-components prior to and/or during use to mitigate the formation of these gaseous inclusions.